cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 112

• Manufacturer Part Number: cn8237
• Description: Atm Oc-12 Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

5.0 Reassembly Coprocessor
5.2 Reassembly Functional Description
5.2.2 Channel Lookup
Figure 5-3. Direct Index Method for VPI/VCI Channel Lookup
5-4
Block Size for VCC Table/
5.2.2.1 Programmable
Base Register (16)
RSM_TBASE
(RSM_ITB)
VPI [11:0]
VCI Index Table
VPI Index Table
VCI_IT_PNTR
The CN8237’s reassembly coprocessor implements a VPI/VCI Index table
mechanism using direct index lookup in order to assign each cell to a virtual
channel, based on its VPI/VCI value. Each channel is thus identified by its
internally generated index value, the VCC_INDEX.
concatenated index values. It simplifies user channel assignment, provides
flexible provisioning for received traffic, and provides fast, consistent lookup
times regardless of the VPI/VCI values. In addition, using VPI/VCI table indexes
minimizes the memory impact in preallocating large numbers of channels by
requiring that only the VCI Index table entries be preallocated instead of the VCC
table entries.
Some users might have a requirement or desire to limit the amount of memory
allocated to VPI/VCI channel lookup. To enable this, the CN8237 provides the
user with the choice of enabling an alternative scheme for the memory allocation
and table handling involved in the Direct Index Lookup mechanism. In this
scheme, the user programs the size of the memory block of RSM VCC table
entries for all VCI Index table entries, to fit a range of 1 to 64 entries, instead of
the default 64 entries.
amount of memory space set aside for RSM VCCs, the total memory space
required for VCC allocation can be substantially lessened.
to a logic high. The SAR will thus allocate block memory for VCC entries per
VCI, based on the value entered in VCI_IT_BLK_SZ (RSM_CTRL1).
This VPI/VCI table Index mechanism dynamically maps VPI/VCIs to
Figure 5-3
Each RSM VCC entry requires 12 words of memory. By thus limiting the
To enable this scheme, set EN_PROG_BLK_SZ in the RSM_CTRL1 register
Mindspeed Technologies
VCI [15:6]
illustrates the direct index channel lookup mechanism.
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
(Max. 1024 entries
VCC_Block_Index
VCI Index Table
for each VPI)
(for one VPI)
™
(RSM_VCCB)
RSM_TBASE
VCI [5:0]
VCC Table Entries)
28237-DSH-001-C
(Block of 64
VCC Table
CN8237
8237_039